The proposed studies will investigate the presence of lymphoblast- associated antigens on lymphoblasts induced by phytohemagglutinin and on lymphoblasts grown in continuous culture. The presence of such determinants will be demonstrated by the stimulation of autologous lymphocytes in mixed leukocyte culture and by the preparation of specific antisera to cultured lymphoblast associated antigens. This reagen will be used to compare the lymphoblast associated antigens on culture, phytohemagglutinin-induced, and leukemic lymphoblasts.